Vapor phase detectors

ABSTRACT

THE CHANGE IN POTENIAL DIFFERENCE, RESISTANCE OR CURRENT FLOW BETWEEN ELECTRODES IN AN ELECTROLYTIC CELL IS UTILIZED TO DETECT PRESSURE CHANGE, ABSOLUTE HYDROGEN PRESSURE AND PRESSURE OF OTHER GASES PRESENT IN HYDROGEN CARRIER GAS, PARTICULARLY THOSE WHICH ARE REACTIVE WITH THE ELECTRODES. AT LEAST ONE OF THE ELETRODES IS FORMED OF A MATERIAL SELECTIVELY PERMEABLE TO HYDROGEN, PREFERABLY COMPRISING PALLADIUM. THE CELL MAY BE SIMULTANEOUSLY UTILIZED FOR SEPARATION AND REGENERATION OF HYDROGEN CARRIER GAS AND MAY BE CONVENIENTLY INTERGRATED AND COMBINED WITH A GAS CHROMATOGRAPHIC COLUMN ON A SMALL SIZE CHIP CONTAINING RECESSES FOR THE CELL AND COLUMN COMPONENTS FORMED BY CONVENTIONAL ETCHINGMASKING TECHNIQUES.   D R A W I N G

Oct. 31, 1972 J. E. LOVELOCK 3,701,532

VAPOR PHASE DETECTORS Filed June 1, 1970 3 Sheets-Sheet l INVENTOR JAMESE. LOVELOCK AT TORNEYS 1972 J. E. LOVELOCK VAPOR PHASE DETECTQRS 3Sheets-Sheet 5 Filed June 1, 1970 NON vow

INVENTOR.

JAMES E. LOVELOCK W,MAM

ATTORNEYS,

'U.S. Cl. 23232 E United States Patent O 3,701,632 VAPOR PHASE DETECTORSJames E. Lovelock, Bowerchalke, near Salisbury, England, assignor toCalifornia Institute of Technology, Pasadena, Calif.

Filed June 1, 1970, Ser. No. 41,905 Claims priority, application GreatBritain, Mar. 5, 1970, 12,003/ 70 Int. Cl. G01n 27/04, 7/10 9 ClaimsABSTRACT OF THE DISCLOSURE The change in potential diflerence,resistance or current flow between electrodes in an electrolytic cell isutilized to detect pressure change, absolute hydrogen pressure andpressure of other gases present in hydrogen carrier gas, particularlythose which are reactive with the electrodes. At least one of theelectrodes is formed of a material selectively permeable to hydrogen,preferably comprising palladium. The cell may be simultaneously utilizedfor separation and regeneration of hydrogen carrier gas and may beconveniently integrated and combined with a gas chromatographic columnon a small size chip containing recesses for the cell and columncomponents formed by conventional etchingmasking techniques.

ORIGIN OF THE INVENTION The invention described herein was made in theperformance of work under a NASA contract and is subject to theprovisions of Section 305 of the National Aeronautics and Space Act of1958, Public Law 85-568 (62 Stat. 435; 42 USC 2457).

BACKGROUND OF THE INVENTION (1) Field of the invention The presentinvention relates to apparatus and methods for analyzing gas samples,and more particularly, to a compact and efiicient detector and gaschromatographic system for analysis of vapor phase constituents ofmicro-size samples.

(2) Description of the prior art Detectors such as the gas densitybalance, the thermal conductivity and ionization cross-section provide asignal related to the concentration of the component to be analyzed.Consequently, any variation in flow rate through these detectors isfollowed by a corresponding change in the sample concentration. Thedetector faithfully follows these changes in sample concentration butthe time integral of the signal will not be an accurate measure of thequantity injected into the system.

Thus, though, these detectors are reliable in isolation, they do noteasily yield accurate analysis when incorporated as components in a gaschromatograph. The conditions for accurate analysis with these otherwiseexcellent detectors, are therefore limited to those in which the carriergas flow rate can be maintained strictly constant. This means that inpractice convenient procedures such as temperature or flow programmingof the column, which almost inevitably are accompanied by some change incolumn flow rate, are accompanied 3,701,632 Patented Oct. 31, 1972 'ice.

be difiicult or impossible to detect. Moreover, the pressure and flowrate of the efiluent emerging from the chromatograph column may exceedthe capability of the detector.

The considerable improvement in analytical capability which may bederived from the combination of gas chromatography and mass spectrometry(GC-MS), has encouraged the development of various interface devices, oras they are more commonly called, molecular separators. These devicesserve primarily as pressure reductionsystems by selectively diminishingthe total mass flow of carrier gas which enters the detector to a levelconsistent with the maintenance of an adequate vacuum. All* of thepresently available separators, with the exception of the Ryhagejet-orifice type rely on a membrane such as plastic or fritted glassthrough which the carrier gas (usually hydrogen or helium), and samplecomponents are separated due to a difierence in their rates of effusionor permeation. The separators are generally enclosed in a vacuum chamberwhich must be continuously pumped to insure efficient removal of theseparated carrier gas. One limitation common to all of these devices isthe loss of some of the sample which invariably accompanies removal ofthe carrier gas.

A much improved technique which relies on the ability of palladiummembranes to totally and selectively remove hydrogen has recently beenreported. Pat. No. 3,638,396, issued Feb. 1, 1972, discloses the use ofa palladium membrane for separating carrier gas from the eflluent of thecolumn for the purpose of sample enrichment prior to detection and alsofor the purpose of reducing efiluent pressure prior to introduction to adetector, such as a mass spectrometer. Use of a palladium membraneseparator in combination with the post column injection of a controlledflow of a second carrier gas, such as helium or a mixture of hydrogenand helium has been disclosed in Pat. No. 3,589,171, issued June 29,1971, and'Pat. No. 3,638,397, issued Feb. 1, 1972.

However, these systems still require the use of heavy carrier gascylinders and essential valving to supply and meter the carrier gases tothe device. A separate source of carrier gas is obviated in the combinedcarrier gas generator-separator disclosed in co-pending application,Ser. No. 7,922 filed Feb. 2, 1970, which utilizes a pair of palladiummembranes which are immersed in a body of molten, electrolyte capable oftransporting hydrogen between the electrodes.

SUMMARY OF THE INVENTION It has now been discovered according to theinvention that the potential difierence, resistance and the current flowin a cell containing an electrode selectively permeable to carrier gasis dependent on the flow rate of carrier gas through the wall of theelectrode. The detectivity of this effect is greatest with compoundsreactive with the wall of the electrode' and the signal is higher whenthe flow of carrier gas through the walls of the electrode is less thansaturation flow rate. This effect may be utilized to detect pressure,changes in pressure, partial pressure of carrier gas or impurity vaporand in cases of specific impurities which provide large signals, it canbe utilized to quantitatively detect the presence of these impurities.

Thus, a single electrolytic cell according to the invention can combinethe functions of carrier gas generation, carrier gas separation anddetection of impurities. A combination with a gas chromatographic columnprovides a complete instrument absent the valving and cylindersassociated with an external supply of carrier gas, and the controls andseparate power supply associated with a separate detector. A completegas chromatograph can be fabricated on a single chip by etchingappropriate recesses for the column and generator-separatordetector andby depositing films of electrode material.

The invention will now become better understood by reference to thefollowing detailed description when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a firstembodiment of a detector according to the invention;

FIG. 2 is a schematic Niew of a further embodiment of the detectordevice utilizing applied potential;

FIG. 3 is a set of chromatograms;

FIG. 4 is a schematic view of a closed circuit chromatographincorporating a generator-separatordetection device according totheinvention;

FIG. '5 is a plan view of an integrated circuit e'mbodiment of thechromatograph-detector system according to the invention;

FIG. 6 is a sectional view taken on the line 66 of FIG.

FIGS. 7-10 are schematic representations of sequential process steps toproduce a variable cross-section chromatograph column; and

FIG. 11 is a plan view of an alternate chem-mill maskant pattern forforming a variable cross-section :colum-n.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The detector according to theinvention generally includes a pair of electrodes, at least one of whichis selectively permeable to carrier gas, a detection circuit and anelectrolyte capable of transporting an ionic species of the carrier gasbetween the electrodes. Referring now to FIG. 1, a simplified detectordevice comprises a container in which is disposed a body 12 ofelectrolyte. The container is provided with a lid 14 formed of anelectrically insulating material which is stable at the temperature ofoperating the device.

At least one of the electrodes, suitab'ly the anode 16 is a hollowtubular body formed of a material selectively permeable to the carriergas. The tubular anode 16 has an inlet 17 for receiving a flow of pureor impure hydrogen carrier gas at a pressure P In the case of hydrogencarrier gas, the anode is formed of palladium or one of its hydrogenpermeable alloys. An external source of heat 1, a simplified detectordevice comprises a container 10 may be utilized to heat the anode to thetemperature at which the anode 16 is permeable to hydrogen and to renderthe body 12 of electrolyte molten.

The second electrode or cathode 20 may be a source of standard potentialsuch as a calomel or silver/silver chloride reference electrode or maytake the form of a hollow tubular body for receiving carrier gas at apressure P An electrical lead 24 is connected to the cathode 20 and asecond electrical lead 26 is attached to the anode 16. A detectioncircuit comprising an :amplifier 28 and a recorder 30 are provided inthe anode lead 16.

When hydrogen is present in the anode 16 and cathode 20 and the heatingcoil 10 is energized to heat the anode tube 16 to a temperature at whichit is permeable to hydrogen and to melt the electrolyte 12 the deviceoperates as a reverse fuel cell developing a potential differencebetween the anode 16 and cathode 20. The, signal developed is amplifiedby amplifier 28 and the amplified signal is recorded on recorder 30.

The potential difference is given by the relationship:

in which:

V is the potential difference in volts; R is the gas constant;

T is the absolute temperature;

F is the Faradays constant; and

H and H are the diiferent carrier gas pressures or concentration ofcarrier gas in the tubular electr des.,In the case of an impurity the Hterms represent partial pressure or concentration of carrier gas.

An initial flow of pure hydrogen carrier gas into the inlet of anodewill provide a first reference signal. Introduction of impurity willchange the hydrogen partial pressure, H and provide a second signalindicative of the quantity of impurity. The impurity will collect inanode tube 16 and can be discarded or further analyzed quantitatively orqualitatively.

A further embodiment of the invention illustrated in FIG. 2 furtherincludes a source of constant potential 32 to form an electrolyticcircuit joining the anode 16 and cathode 20. The anode circuit mayinclude a current detector 35. The anode is in the form of an open endtube 31 having an inlet 34 for receiving a flow of impure carrier gasand an outlet 36 for elimination of collected impurity.

Application of a potential from source 32 to the anode 16 and cathode 20results in hydrogen separation by diffusion through the wall of theanode 16, across the body 12 of electrolyte and through the wall ofcathode 20. The impurities collected within the anode tube 16 and arewithdrawn through outlet 36 and the hydrogen regenerated in the cathode20 is removed through outlet 38..

The generator-separator-detector of this embodiment has several uniquefeatures. It resides in the combination within an electrolyte of apalladium tube cathode able to generate hydrogen with a palladium tubeanode able to return it to the electrolyte. Thus, both electrodes aresimilar and elfectively are both hydrogen electrodes. Hence, thepotential of the cell tends to zero. The power needed to generatehydrogen at the cell cathode, recirculate it to the anode and remove itat the anode is very much less than would be required to producehydrogen by electrolysis. This is because the cell is in :a sense a fuelcell operated in reverse. To generate 696 cc. of hydrogen per minute byelectrolysis requires 1.55 watts. To circulate 6.96 cc. of hydrogen perminute through the generatorseparater of FIG. 2, needs only 0.2 watt.

Pure palladium when subject to temperature cycling in the presence ofhydrogen, suffers mechanical distortions. However, an alloy of palladiumcontaining 10% to 30% silver, preferably about 25% silver is aspermeable to hydrogen and is mechanically stable. Other palladiumalloys, for example, palladium-rhodium or palladium-gold alloys mayconfer more resistance to corrosion to the films and extend the usefullife of the generator-separator, but are less permeable to hydrogen. Thepalladium tube may be provided in various configurations and lengths oftubing may be connected in parallel to provide increased surface areawith less flow resistance. Membranes or tubes can also be formed from abase structural material such as a porous ceramic coated with a thinfilm of palladium or a suitable hydrogen permeable palladium alloy.

The hydrogen flux through a film of palladium for a given hydrogenpressure is dependent on tube geometry, wall thickness and walltemperature. The flux of hydrogen through the wall of a tube heated inair or oxygen to temperatures in the range of C. to 350 C. is 0.1 torrliters sec.- /cm. The electrolyte provides a convenient oxidizingenvironment for effecting this pumping. The cell is suitably operated ata temperature of 200 to 250 C.

The film may be maintained at a hydrogen permeable temperature byexternal heating means or by heating the device electrically. Asillustrated, the coil 18 may be utilized to raise the temperature of theanode tube 16, cathode tube 20 and electrolyte 12 to a temperature above200 C.

Though it is desirable to maintain the resistance of the electrodes andelectrolyte as low as possible for purposes of electrical powerefliciency, the electrolytic cell may in some configurations provide asufficient internal impedance to produce the desired heating on passageof current through the electrodes and electrolyte. In otherconfigurations, the heat supplied by operation of the electrolytic cellcontributes to the heat required to maintain the films at the desiredtemperature. Thus, the electrolysis current supplied by the potentialsource 32 may also be utilized to provide a portion of the necessaryheating.

The electrolyte is a material capable of transporting an ionic speciesof the carrier gas from one electrode to the other, is inert withrespect to the electrodes, is stable at the temperature of operation andis capable of regenerating the carrier gas by electrolytic associationor disassociation as is required. The electrolyte may be an acid, basicor salt material and is preferably an inorganic metal hydroxide.

The most suitable material for use in the invention are the Group Imetal hydroxides such as sodium hydroxide, potassium hydroxide, orlithium hydroxide. The hydroxides may be utilized in the unhydrated orhydrated form, suitably containing to 35% water of hydration since thisboth lowers the power requirement and the temperature at which theelectrolyte becomes molten. Improved operation of the cell occurs whenat least 10 to 25% of the lighter weight lithium hydroxide is mixed withsodium or potassium hydroxide, preferably the latter. Commercialpotassium hydroxide containing 25% water melts at 275 C. The addition of10% lithium hydroxide vto this electrolyte further lowers thetemperature at which the electrolyte becomes molten to about 200 C.

The ionic and water content of the electrolyte is also maintainedconstant during operation. The OH- ion which is liberated ondecomposition of water at the cathode recombines with the H+ ionsentering the system to form water which maintains the hydrationconcentration of the electrolytic cell constant. For this reason, it ispreferred to maintain an excess of hydrogen protons in the system at alltimes to prevent the formation of molecular oxygen which will causebubbles in the electrolyte and excessive pressure on the thin wallelectrode tubes.

When the device is polarized at a fixed potential, preferably from a lowimpedance source, the current flow in the cell changes as the partialpressure of hydrogen in the anode changes. The detectivity of thiseffect is the largest when the flow of hydrogen through the walls ofanode tube 16 is limited, i.c., when the metal is not saturated withhydrogen. Thus, a separate, higher sensitivity detection circuit can beprovided by inserting an electrical insulator sleeve 38, suitably formedof Teflon (polytetrafluoroethylene), to electrically isolate the lastseg ment 40 is below saturation and the signal in current detector 37 issubstantially larger than the signal in current detector 35.

vThe detection mechanism is believed to be a result of throttling of thehydrogen flow to the anode electrode interface resulting from thediminution of hydrogen concentration by the molecules of the detectedsubstance. Another mode of detection is the change in electricalresistance which accompanies the permeation of the metal wall of theanode by hydrogen. This effect, unfortunately, is the least with thepalladium-silver alloys which are most commonly available. Theconductivity or resistance detector would also observe compounds interms of the hydrogen they displace in the gas phase or the hydrogenthey prevent from entering the metal wall of the anode electrode. Thegas volume of either type of detector can be as small as a fewnanoliters and would be the smallest detectors available suitable forgas chromatography.

The power of the signals developed is unusually large even for partialpressure effect. FIG. 3 is a chromatogram of a mixture of helium, argon,nitrogen and-methane using the cell as a detector. The nitrogen peak forexample, represents a deflection of milliamperes. A list of compoundswhich pass through the palladium-silver tube unaltered is provided inthe following table.

" TABLE I Hydrocarbons:

Hexane l-hexene 2-hexene Cyclohexane Cyclohexene Benzene 2 methyl,2-hexene Alcohols: I n-Propyl alcohol Phenol Benzyl alcoholCy'clohexanol Ketones:

'- Methyl ethyl ketone Cyclohexanone Acetophenone Furan 2,4-pentanedioneEthers:-

'Diethyl ether" Tetrahydrofuran Anisole Aldehydest' PropionaldehydFurfural Benzaldehyde Esters:

Ethyl acetate Methyl laurate Nitrogen compounds:

Methyl amine Benzonitrile Phenyl' acetonitrile Pyrrole Pyridine.Ethanenitrile Sulfur compound:

Thiophene Halogen compounds:

' Butyl chloride Chlorobenzene I Perfiuoropentane Gases:

- "Carbon dioxide Carbon monoxide Methane Argon Nitrogen Nitric oxideNitrogen dioxide Nitrous oxide The inner surface of the heated palladiumtube is catalyticto many substances which react therewith withdevelopment of even larger signals. Examples of such compounds arereducible compounds as listed in the table below:

v v TAB LE II Starting compounds Hydrogenated product Percent AeroleinPropionaldehyde. 96. 7 Acrylonltrlle. Propanem'trile. 96. 1 Methylaerylate. Methyl propanoate 97. 5 Methyl vinyl ket0ne- Methyl ethylketone 92. 1 Isoprene 2 methyl, l-butene 93. 0 2,4 hexadlene. Hexene 97.2 1,5 hexadiene I o 87. 2 Styrene Ethyl benzene l 95. 0 AcetyleneEthylene plus polymer 90. 0 Water 99. 0

Oxygen .Z-

The largest signals are developed on passage through the anode-separatortube of compounds which reversibly adsorb or poison the catalyticactivity of the palladium surface such as carbon monoxide, nitrous,oxide, and sulfur containing gases such as hydrogen sulfide, sulfurdioxide, and mercaptans'; and iodine compounds such as ethyl iodide. Thecharacteristic deflection of these peaks can be utilized toqualitatively detect the presence of particular compounds. A thresholdsensor may be incorporated in the detector for this purpose.coincidentally, the reactive detectable compounds happen to be majorconsituen-ts of air pollution and thus the detector of the invention isunusually suitable for air pollution detection and control.

Concentrations of less than 500'p.pm. of the sulfur containing gases inthe carrier streams caused temporary poisoning of the surface in oneexperimental device. Higher concentrations caused progressive loss ofhydrogen separation efliciency and repeated injections of thesecompounds at a concentration of 5000 p.p.m. may render the separatorinactive. Activity can be restored by heating the separator anode to 500C. for several hours; Palladiumgold alloys are less susceptible topoisoning by sulfur compounds but are generally less permeable tohydrogen. The flow of hydrogen from the cathode can be turned on,controlled or stopped simply by analogous changes in the currentsupplied to the cell. Storage cylinders, gas purifiers, flow andpressure regulators are all unnecessary. The anode can function as atransmodulator or a mass spectrometer separator if desired. The cathodecan generate hydrogen pressures up to at least 500 p.s.i. so that allthe needs of a gas chromatograph column in terms of flow and pressurecan readily be met without the need for pneumatic control valves.Procedures such as flow or pressure programming can be effected fromelectrical analogue instruction externally impressed on the cell. Inaddition, the usual disadvantages of flow and pressure programmingnamely their adverse effect on detector performance due to large changesin carrier gas flow rate are not a problem.

When combined with a gas chromatograph preferably in a closed loop manyother advantages are realized. The cell can replace the conventional gaschromatograph detector. Since the electrolytic cell also functions as acarrier gas generator and separator, all that is required to complete agas chromatograph is the column, a sample inlet and suitable valving.Such a system is illustrated in FIG. 4.

The system generally includes a generator-separatordetector cell 50, agas chromatograph column 53; a current indicator 54 and suitablevalving, piping and wiring. The cell 50 comprises a container 56suitably formed of Teflon (polytetrafluoroethylene) having a lid 58. Abody 60 of electrolyte is received within the container 56 and a heatingcoil 62 suitably a Nichrome wire heating element, surrounds the sidewall of the container 56. A tubular cathode 64 having a closed bottom 66is immersed in the electrolyte 60. An anode in the form of a'helicalcoil 68 is supported symmetrically around the' cathode 64 by means ofinsulating spacing strips 70, suitably formed of Teflon. The anode 68and cathode 64 are mounted through apertures in the Teflon lid 58.

External connections are made to the. palladium tubes by brazing withpure silver in a hydrogen atmosphere. It is important to ensure that nometal, other than palladium alloy or the noble metals is in contact withthe electrolyte. The performance of the cathode is impaired if othermetals are electrolytically deposited upon its surface; iron and nickelappear to be particularly detrimental in this respect.

7 The electrolyte used was KOH 67.5%, LiOH 10.0% and water 22.5% and wasmade by adding 10 gms. of LiOH to 90 gms. of KOH pellets, containing .25water. This mixture could be used over the temperature range 160 to 250C., usually 230 C. The LiOH served to lower the melting point,particularly at the cathode surface where water is removed byelectrolysis and solid sheaths of KOH might otherwise tend to form.Before it was added to the cell, the electrolyte was electrolyzedbetween platinum electrodes at 0.01 ampere for 8 hours to remove tracesof ferrous and other metals.

The cathode electrode 64 is connected to the negative terminal of a lowimpedance, constant potential source 74 and the anode electrode 68 isconnected through a current measuring and recording device 76, suitablyan electrometer amplifier and a potentiometer recorder, to the positiveterminal of source 74. Higher efliciency and reduced electrolyticconversion are provided by electrically joining the inlet and outlet ofthe anode so that the effective length of the anode tube along whichthe'electrical current must flow is halved.

A chromatograph column 52 is connected across the anode 68 and cathode64 such that the outlet 80 of the column communicates with the inlet 82to the anode 68 and the outlet 84 of the cathode communicates with theinlet 86 to the column. A sample inlet branch conduit 88 contains avalve 90 and is disposed in the line 92 joining the cathode outlet 84and column inlet 86.

The column 52 consists of a series of reactants which segregate the gassample by affecting the rate at which the different constituents of thegas sample flow through the column to provide an effluent containing asequential passage of the constituents.

The device is operated by energizing the power source, preferably to apower level of less than about 0.6 volt for the present configurationand energizing the coil 62 to heat the electrolyte to a temperature ofabout 230 C. Hydrogen carrier gas Within the anode 68 is transferredthrough the wall of the anode, across the electrolyte 60 and through thewall of the cathode and collects within the cathode 64.

When sufficient pressure is developed in the cathode 64, the hydrogencarrier gas flow through line 92 and sweeps past branch conduit 88 anddraws sample through valve 90. The carrier gas propels thesample-carrier gas mixture through the column 52. The efiluent leavesthe column through outlet 80v and enters the inlet 82 of the anode 68.Most or all of the hydrogen is removed through the anode tube wall andcollects in cathode 64 for recycling to the column 52. The currentflowthrough the cell as indicated on recording device 76 drops when asample constituent emerges in the efiluent from the column 52 and entersthe anode 68.

The invention further renders possible the construction of amicrominature gas chromatograph in which all the elements including thecolumn could be formed on a small chip which need not be over 1 cm. by'2cm. in overall size, utilizing techniques well established infabrication of microelectronic and integrated circuit" devices.

Referring now to FIGS. 5 and 6, the device is formed on a pair of planarchips and 102 of a material which is impervious to gas, preferably hashigh electrical resistance, is a good thermal insulator, is resistant toattack by the molten electrolyte and is stable 'at the temperature ofoperating the device. Suitable materials are refractory metal oxidessuch as magnesium oxide or high temperature, inert plastics such asTeflon (polytetrafiuoroethylene). The various recesses and channels maybe formed by conventional machining or etching techniques. The planarsurface may be covered with a film of chem-mill maskant. Portions of thefilm are'cut and peeled to expose the surface areas to be etched to formthe recesses. After removal from the etchant bath, the remainder of thefilm is stripped from the surface of the chip.

The device contains a column section 104, an electrolytic cell section106, which are joined by a sampler section 108. The column section 104is an elongated channel which has been folded to conserve space. Theinside surface of the channel may be lined with a film 112 of adsorbentor retardant, either liquid or solid, suitably a molecular sieve or asilicone oil. The inlet,,114 to the column communicates with the outletconduit channel 116 from the sampler section 108. The outlet channel 119of the column delivers the column effluent to the inlet 7 144 to chamber142 of the cell 106.

"The sampler-section comprises a fixed volume recess forming a chamber118. The outlet conduit channel 116 also communicates with sample inletport 120 through sample valve 122. To load the chamber 118, the hydrogenin'it is removed by reversingthe polarity to the cell 106 in a brieflarge pulse. The sample valve 122 is opened and sample drawn into thechamber 118 and thev sample valve is then closed. The inlet 124 to thesample chamber 118 is connected to the output of the cathode ucompartment 154.

' The cell includes a folded recess forming an electrolyte compartment128 containing a body of electrolyte 130.

The outside surface of the electrolyte compartment is 138 voneach endthereof which is fitted and sealed into grooves 140 formed in the chips100 and 102 adjacent the compartment 128. An anode chamber 142,surrounds the .anodefilm 132. The anode chamber 142 is defined by theoutside surface of the anode film 132 and the opposing wall surfaces ofthe chips 100, 102. The inlet 144 of the anode chamber 142 receives theeffluent from the outlet channel 119 of the colum 110. The outlet fromthe anode chamber 142 is exhausted through a vertical vent aperture 146provided chamber 142.

The inner wall of the electrolyte compartment 128 is formed by a secondfilm 152 of palladium-silver alloy which functions as the cathode. Acathode chamber 154 is provided adjacent the outside surface of film152, and opposing surfaces of recesses formed in the chips 100, 102. Theoutlet of the cathode chamber 154 is connected to the inlet 124 tosampler chamber 118. The palladiumsilver films may be preformed andinstalled into the grooves or may be formed in situ utilizing vacuumdeposition or photo-etching techniques.

A separator anode lead 160 and cathode lead 162 connect the separatoranode 132 and cathode 152 respectively to the positive and negativeterminals of a constant potential, low impedance power source, 170. Adetector lead 164 connects the detector anode 136 to an indicator 166.

A heat source for the device may be provided by means of strips 168 ofhigh resistance metal vacuum deposited onto at least the bottom surfaceof chip 100 and connected to a power source and controller not shown.After the appropriate channels are formed in chips 100, 102, they areassembled by applying sealant to exposed original planar surfaces tobind the chips together and to form gas tight seals for the variousrecesses, channels and compartments.

The continuous circuit for operation is similar to that described withrespect to FIG. 4. The introduction of sample has been discussed. Onapplication of normal polarity to the cell section 106 hydrogen producedin the cathode compartment 154 will enter the sample chamber 118 andsweep the sample through column 110. The effiuent from the column 110will enter the anode compartment 142 and hydrogen will be separated bydiffusion through anode film 132, electrolyte 130 and cathode film 152and will collect in cathode chamber 154. The hydrogen will besubstantially depleted by the time it reaches the detection anode 136and a large signal will be detected on indicator 166. Impurity vapor isexhausted through vent aperture 146.

Since the column could be produced on the chip by methods available fromthe integrated circuit, or chemmill art, it would be possible to form acolumn having any desired cross-sectional configuration. This would makeit possible to devise the capillary column in a configuraat the outletend 148 of the anode 1s coated with a peelable film 202 of chem-millmaskant,

tion which would provide the advantages of flow programming withoutchanging temperature or flow rates. This could be accomplished byproviding a variable cross- A section which increases or decreases withdistance along the column in accordance with a predeterminedrelationship. The column would then produce a chromatogram having peaksdistributed linearly in time. In contrast the uniformly cross-sectioned,conventional column produces peaks distributed logarithmically.

Since this advantage is feasible using microminiature techniques, itfollows that the same techniques could be utilized, on a larger scale,to fabricate a column on a larger substrate, having a, cross-sectionvarying as mentioned.' Thus, it would be possible to fabricate columnsfor conventional gas chromatographs having unique crosssectionalconfigurations which are now not feasible either technically oreconomically to produce from metal tubing.

Referring now to FIGS. 7-17, differential etching techniques may beutilized to form variable cross-section columns. In FIG. 7, a planarchip 200 of etchable material such as the diene elastomer materialsdescribed in US. Pat. Nos. 2,888,335, 3,079,352 and 3,227,589. Scribelines 204 are cut in the film 202 on the top surface of the chip 200 inthe form of uniformly tapering and converging lines. The interiorV-shaped portion 206 of film 202 is peeled and stripped from thesurface.

In FIG. 8, the chip is exposed to an etchant solution, 208, suitably anacid in the case of magnesium oxide. The etchant differentially etchesthe chip to form a semiconical diverging channel 210 as shown in FIGS. 9and 10. Two mating chips so processed are joined to form a column.

A further form of a variable cross-section chromatograph column isillustrated in FIG. 11. The scribe lines 204 define a series ofdecreasing diameter column lengths. When processed by differentialetching, the exposed portion within the scribe lines will form acorrespondingly shaped column.

It is to be understood that only preferred embodiments of the inventionhave been described and that numerous substitutions, modifications andalternations are all permissible without departing from the spirit andscope of the invention as defined in the following claims.

What is claimed is:

1. A vapor phase analysis instrument comprising:

a first palladium containing electrode film impermeable to gas when coldand selectively permeable to hydrogen gas when heated having a firstsurface and a second surface;

a second palladium electrode film impermeable to gas when cold andselectively permeable to hydrogen gas when heated having a first surfaceand a second surface;

compartment means adjacent the first surface of said first film havingan inlet for applying a dispersion of impurity in said hydrogen gas tothe first surface of the first film;

closed chamber means defined between said second surfaces;

a body of electrolyte capable of transporting hydrogen between saidfirst surfaces received in said chamber means in contact with saidsecond surfaces;

potential means for applying electric potnetial to said films and saidelectrolyte to selectively transfer hydrogen through said first film,across the electrolyte and to generate hydrogen through the second film;and

current indicator means connected to said first film for detectingchanges in current flow through said first film related to changes inconcentration of impurity in said dispersion and the hydrogen transferrate through said first film.

2. An instrument according to claim 1 further including a separatedetector electrode film selectively perme- 11 able to hydrogen gas, saidfilm being disposed within a wall of said chamber means, and having asurface in contact with the body of electrolyte and a surface isolatedfrom said electrolyte.

3. An instrument according to claim 1 in which the current detector isconnected to said film at a location of the film at which the hydrogengas flux through the film is less than the saturation flux.

4. A method of detecting a gaseous comprising the steps of:

contacting. a first face of a first and second palladium electrode filmimpermeable to all gases at a first temperature and selectivelypermeable to hydrogen at a temperature above the first temperature witha body of electrolyte capable of transporting hydrogen between thefilms;

heating the films to a temperature above the first temperature; applyinga potential difference to said films sufficient to electrolyticallytransfer hydrogen between said films;

flowing a dispersion of said substance in hydrogen carrier gas incontact with the obverse surface of said first film and selectivelytransferring hydrogen through the first film into the electrolyte andthrough the second film; and

measuring the change in an electrical parameter of said first filmresponsive to changes in the concentration of the substance in thedispersion and the transfer rate of hydrogen through said first film.

5. A method according to claim 4 in which the fiow rate of hydrogenthrough said first film controls the cura 12 rent flowing between saidfilms and this current is measured as said parameter.

6. A method according to claim 5 in which said measurement is made at aportion of said first film in which the hydrogen flow rate is belowsaturation.

7. A method according to claim 4 in which the partial pressure ofhydrogen carrier gas is reduced by introducing an impurity gas into saidcarrier gas.

8. A method according to claim 7 in which said impurity is reactive withsaid first film.

9. A method according to claim 8 in which said impurity is a substancewhich reacts said first film to form a substance which at leasttemporarily poisons the surface of said film.

References Cited MORRIS O. WOLK, Primary Examiner R. E. SERWIN,Assistant Examiner US. Cl. X. R.

23254 E; 7327 R, 29; 204 P

